Direct-acting pressure and vacuum sensor

ABSTRACT

A direct-acting pressure and vacuum gauge operable in the lowpressure range and constituted by two cantilever springs having different lengths and spring rates. The two springs have similar curved formations and are maintained in spaced relation one within the other, to define a pressure region therebetween. Both springs are attached at one end to a fixed input socket, the free ends of the springs terminating in a common head from which a pointer is extended. Disposed within the pressure region and abutting the inner walls of the springs, is a flexible bladder forming an internal chamber communicating with the socket, whereby fluid fed into the chamber causes the springs to deflect as a function of fluid pressure, thereby moving the pointer to indicate pressure.

Unite States Patent 1 1 Schmaus et a1.

[54] DIRECT-ACTING PRESSURE AND VACUUM SENSOR [751 Inventors: SiegfriedH. A. Schmaus, Philadelphia, Pa.; Franklin G. Reick, Westwood, NJ.

[73] Assignee: said Schmaus by said Reick 22 Filed: Sept. 3, 1971 [21]Appl. No.: 177,619

Related U.S. Application Data 7 [63] Continuation-impart of Ser. No.317. Jan. 2, 1970.

[52] US. Cl ..73/418, 73/411 [51] Int. Cl. ..G0ll 7/04 [58] Field ofSearch ..73/418,411,412,

[56] References Cited UNITED STATES PATENTS 1,421,501 7/1922 Kraft eta1. "73/396 3,603,153 9/1971 Schmaus ..73/411 Primary Examiner-Donald O.Woodie] A tt0rne v Michael Ebert [57] ABSTRACT A direct-acting pressureand vacuum gauge operable in the low-pressure range and constituted bytwo cantilever springs having different lengths and spring rates. Thetwo springs have similar curved formations and are maintained in spacedrelation one within the other, to define a pressure region therebetween.Both springs are attached at one end to a fixed input socket, the freeends of the springs terminating in a common head from which a pointer isextended. Disposed within the pressure region and abutting the innerwalls of the springs, is a flexible bladder forming an internal chambercommunicating with the socket, whereby fluid fed into the chamber causesthe springs to deflect as a function of fluid pressure, thereby movingthe pointer to indicate pressure.

9 Claims, 6 Drawing Figures DIRECT-ACTING PRESSURE AND VACUUM SENSORRELATED APPLICATION This application is a continuation-in-part of thecopending application Ser. No. 000317, filed Jan. 2,1970.

BACKGROUND OF INVENTION This invention relates generally todirect-acting pressure and vacuum sensors, and more particularly to apressure gauge of the elastic type which is operable in the low-pressurerange.

Measurement of absolute pressure, gauge pressure, vacuum and draftpressures, and differential pressure, is carried out by two primarytypes of pressure-sensitive elements, the first being the liquid columnin which the height'and density of the liquid are utilized to measurepressure, and the second being the elastic pressure device. The soleconcern of the present invention is with elastic pressure elements whichare designed to follow the physical law that within the elastic limit,stress is proportional to strain; hence deflection is proportional toapplied pressure.

The Bourdon tube, because of its stability, simplicity and high pointertorque, is widely used as a pressure or vacuum indicator or controller.The operation of the Bourdon tube is based on the principle that anelastic tube having an internal cross-section that is not a perfectcircle, if bent or distorted, has the property of changing its shapewith internal pressure variations. This internal pressure causes thecross-sectional form to become more circular, giving rise to a motion ofthe closed end of the tube if the open end is rigidly fixed. This motionis called tip travel.

The Bourdon tube comes in three main types. The C-type is formed bywinding the tube to define a segment of a circle, whereas the spiraltype is created by winding more than one turn of the tube in the shapeof a spiral about a common axis. The helical type is created' by windingseveral turns of the tube in the shape ofa helix. A Bourdon spring inany of the existing types can be made from any metal or alloy whichexhibits satisfactory elastic qualities.

While Bourdon types of the C, spiral, or helical type are capable ofoperating within various pressure ranges running as high as 100,000 psi,in no instance is it possible as a practical matter, to operatesuchtubes below 12 or psi. Hence, despite the advantages of Bourdontubes, they are not effective as gauges in the low-pressure range. I

SUMMARY OF INVENTION I In view of the foregoing, it is the primaryobject of this invention to provide a direct-acting pressure and vacuumsensor of the elastic type, which is capable of operating in thelow-pressure range.

The need for inexpensive pressure sensors in the lowpressure range iswidespread. Thus the need exists for such devices in the followingapplications, among others:

a. pressure gauge for motor-boat speedometer;

b. air Gauge;

c. receiver gauge for process control;

d. low-pressure switches; e. level indicators; f. vacuum Gauge A morespecific object of the invention is to provide a simple, stable andreliable pressure and vacuum sensor which may be manufactured at lowcost, the sensor being responsive to low-level pressure or vacuum valuesto carry out indicating or control functions.

Briefly stated, these objects are accomplished in an elastic device forsensing or measuring pressure levels, particularly low-pressure levels,the device being constituted by two cantilever springs of differentlength and spring rate, the two springs having a similar C or othercurved formation and being maintained one within the other, in spacedrelation to define a pressure region. Disposed within the pressureregion and abutting the springs is a flexible bladder forming aninternal chamber. One end of the two springs is attached to a fixedsocket communicating with the internal chamber, the free end of thesprings terminating in a common head from which a pointer extends. Fluidfed through the socket to the internal chamber causes deflection of thesprings as a function of fluid pressure, thereby shifting the pointer toan extend depending on the level of pressure.

OUTLINE OF THE DRAWING For a better understanding of the invention, aswell as other objects and further features thereof, reference is made tothe following detailed description to be read in conjunction with theaccompanying drawings, wherein:

FIG. 1 illustrates, in side view, a direct-acting pressure gauge inaccordance with the invention;

FIG. 2 is a section taken in the plane indicated by line 2-2 in FIG. 1;

FIG. 3 is a section taken along the line 33 in FIG.

FIG. 4 is a section taken through the line 44 in FIG. 1; I

FIG. 5 is a perspective view of the bladder; and FIG. 6 illustrates theoperating principles of the gauge.

DESCRIPTION OF THE INVENTION Referring now to the drawing, and moreparticularly to FIG. 1, there is shown a preferred embodiment of theinvention in the form of a 3 to 15 PSI receiver gauge. In the Figure,pointer 10 is shown at the midpoint of an arcuate scale 11, hence at 9PSI.

The gauge includes a pressure-responsive subassembly generallydesignated by numeral 12, anchored on a socket 13. The socket issupported on the rear wall 14A of a frame 14 covered by a casing 21, thescale 11 being visible through an opening in the front wall of thecasing. Socket 13 is coupled to a hose connector l5 projecting from therear wall of the frame, whereby fluid under pressure may be admittedinto the sub-assembly.

A mounting bracket 148 secured to the rear wall 14A of the frame, makesit possible to mount the gauge behind an instrument panel or otherdisplay surface. By suitable bracket arrangements, one may mount thegauge at any other desired position.

Sub-assembly I2 is constituted by two flat springs 16 and 17, bothhaving the same width but differing in length, so that the springs,which may be made of any suitable metal or alloy of the types currentlyemployed in Bourdon tubes, have different spring characteristics orspring rates.

Springs 16 and 17, which may be of metallic or plastic material, bothhave a similar C-formation, the free ends thereof being sharply bent toextend laterally in overlapping relation and being joined together by arivet 18 serving as the common head of the subassembly.

Secured by the rivet 18 to the common head is the stem A of pointer 10,so that as the head is deflected as a function of applied pressure, thepointer is shifted along its scale to indicate the level of pressure. Inpractice, stem 10A may be an extension of spring 16 rather than aseparate element. It will be appreciated that various other expedientsmay be used to indicate the extent of head deflection, which expedientsmay be nonmechanical or electrical in nature to provide an analogvoltage indicative of pressure.

Rivet 18 maintains the springs in spaced relation to define therebetweena pressure region which is occupied by a flexible bladder 19 formed ofnon-permeable material that abuts the inner surface of both springs. Thebladder preferably is fabricated of a material minimizing frictionalcontact with the springs in the course of deflection.

The other end of springs 16 and 17 is secured to socket 13 by means of ascrew 20 that passes through a circular opening 19A (see FIG. 5) inbladder 19. Sealing gaskets 21 and 22 are mounted on the shank of screw20 on either side of the sub-assembly, and a spacer 23 is interposedbetween the walls of the envelope, the spacer having a clearance channel23A therein for passing fluid from the socket into the internal chamberof the bladder. The shank of screw 20 has a flattened portion 20A topermit passage of fluid into the internal chamber.

Because of the different lengths and spring rates of the springs in thesub-assembly including the bladder, the sub-assembly as in the case ofaC-shaped Bourdon tube, is deflected as a function of applied pressure.In an arrangement wherein the inner spring 17 is thin relative to outerspring 16, the device is adapted to act as a vacuum sensor. But when thesub-assembly is intended for use as a gauge for internal pressureapplications, the spring arrangement is then reversed, whereby thethinner spring is on the outside while the thicker spring is on theinside. Obviously, in either application, the thinner spring should bekept under tension. In some instances, one may operate with springs ofthe same thickness.

For purposes of calibration, the effective length of the springsrelative to each other, may be adjusted in the manner described in theabove-identified copending application. It is not necessary to use flatspring material, and in practice the springs may be wirelike or in othercross-sectional configurations, such as trapezoidal. Also, instead ofbending the springs into a C-formation, as shown in the Figures, thesprings may be caused to assume a spiral or helical formation, with asuitable bladder interposed between the spaced springs.

Bladder 19, as best seen in FIGS. 4 and 5, has a strip formation, and isof sufficient length to occupy the pressure region between springs 16and 17. The bladder has a rectangular or oblong cross-section defined bysubstantially parallel upper and lower walls 19A and 19B, separated byan internal chamber 19C. The anchored end 19D of the bladder is cut oneither side to form a closure tip which, as shown in FIG. 1, extendsbelow the socket 13, whereas the other or free end 19E is cut at rightangles to the long axis of the bladder so that it fits neatly betweenthe free ends of the springs.

The bladder is preferably in the form of a reinforced rubber or neopreneenvelope, whose surface is treated to minimize friction with theabutting inner surfaces of springs 16 and 17, for such friction may leadto undesirable hysteresis effects.

In practice, a bladder having these characteristics may be made by meansof a mandrel in the form of a piece of Teflon tube having a flat metaltongue inserted therein to cause the tube to assume a flattenedformation. A fabric sleeve, preferably woven of Dacron or otheroriented, non-reactive, synthetic yarn material of high strength, isslipped over the mandrel and caused thereby to assume a similar shape.

The sleeve is then impregnated with a moisturecuring silicone rubbersolution, such as Dow Chemicals 92909 Disperson Coating, and theimpregnated sleeve is then placed in a hydrostatic press and subjectedto pressure to force the impregnant well into the pores of the fabric.

After the mandrel is withdrawn, the ends ofthe fabric sleeve are cut totheir required shape and are coated with the same solution, to seal offthe ends. In order to provide surfaces having exceptionally low-frictioncharacteristics, a uniform layer of minute glass balls is coated ontothe faces of the bladder, using the same silicone rubber solution, thistime as a binder for the glass balls.

The rounded, smooth glass balls which, in operation, engage the innersurfaces of the springs, act as lowfriction bearings. In order to avoidabrasion of the metallic surfaces by the glass balls, these surfaces arecoated with Teflon, graphite or other lubricating or high-slippagematerial. As a consequence, the frictional engagement between the metalsprings and the bladder is markedly reduced, and hysteresis effectsavoided, whereby despite the simplicity and inexpensive nature of thegauge structure, it is highly accurate.

In order to provide a simple analysis of the gauge action, we now referto FIG. 6, showing the sub-assembly apart from the frame. The innerspring is represented by L,, and the outer spring by L The free end ofthe springs is joined at the common head A, the other end being anchoredat B. Both springs L, and L are uniformly loaded by the internalpressure in bladder C.

Spring I.. being longer, has a larger effective area than L Pressureapplied internally to bladder C, will impose a load uniformly on springsL and L causing head A to move in direction X, because of thedifferential forces applied to common head A. The extent of movement isproportional to applied pressure, this action being linear in that noappreciable degree of friction exists between the surfaces of thesprings and the bladder.

While there has been shown and described a preferred embodiment ofdirect-acting pressure and vacuum sensor in accordance with theinvention, it will be appreciated that many changes and modificationsmay be made therein without, however, departing from the essentialspirit of the invention.

We claim:

1. A pressure sensor for fluids, comprising:

A. first and second cantilever springs having different lengths andspring rates, the first spring being longer than the second spring saidsprings having similarly-curved formations and being maintained inspaced relation, the second spring being disposed within the firstspring, said springs having opposing inner surfaces to define a curvedpressure region therebetween,

B. a common head interconnecting free ends of the first and secondsprings,

C. a fixed fluid input socket anchoring the other ends of the springs,

D. a flexible bladder occupying said curved pressure region and havingan internal chamber, external surfaces of said bladder engaging theopposing inner surfaces of said springs, said internal chambercommunicating with said fluid input socket to be filled with pressurizedfluid causing said bladder to change curvature and impose a load on saidsprings whereby fluid introduced therein causes deflection of saidsprings to shift said common head to an extent depending on the level offluid pressure; and

E. means coupled to said head to indicate said level of pressure.

2. A sensor as-set forth in claim 1, wherein said springs have aC-formation.

3. A sensor as set forth in claim 2, wherein said indicating means is apointer whose stem is attached to said common head and is movable alongan arcuate scale.

4. A sensor as set forth in claim 3, wherein said scale is disposed onthe front end of a rectangular casing whose rear wall supports saidsocket.

5. A sensor as set forth in claim 4, further including a hose connectorprojecting from the rear wall of the casing and coupled to said socket.

6. A sensor as set forth in claim 1, wherein said bladder is formed by areinforced rubber envelope.

7. A sensor as set forth in claim 6, wherein said reinforced rubberenvelope is defined by a woven fabric sleeve impregnated with siliconerubber.

8. A'sensor as set forth in claim 6, wherein said envelope has a layerof minute glass balls bonded to the external surfaces thereof to reducefriction with the surfaces of the springs engaged thereby.

9. A sensor as set forth in claim 8, wherein the surfaces of the springsengaged by the balls are coated with a high-slippage substance.

1. A pressure sensor for fluids, comprising: A. first and secondcantilever springs having different lengths and spring rates, the firstspring being longer than the second spring said springs havingsimilarly-curved formations and being maintained in spaced relation, thesecond spring being disposed within the first spring, said springshaving opposing inner surfaces to define a curved pressure regiontherebetween, B. a common head interconnecting free ends of the firstand second springs, C. a fixed fluid input socket anchoring the otherends of the springs, D. a flexible bladder occupying said curvedpressure region and having an internal chamber, external surfaces ofsaid bladder engaging the opposing inner surfaces of said springs, saidinternal chamber communicating with said fluid input socket to be filledwith pressurized fluid causing said bladder to change curvature andimpose a load on said springs whereby fluid introduced therein causesdeflection of said springs to shift said common head to an extentdepending on the level of fluid pressure; and E. means coupled to saidhead to indicate said level of pressure.
 2. A sensor as set forth inclaim 1, wherein said springs have a C-formation.
 3. A sensor as setforth in claim 2, wherein said indicating means is a pointer whose stemis attached to said common head and is movable along an arcuate scale.4. A sensor as set forth in claim 3, wherein said scale is disposed onthe front end of a rectangular casing whose rear wall supports saidsocket.
 5. A sensor as set forth in claim 4, further including a hoseconnector projecting from the rear wall of the casing and coupled tosaid socket.
 6. A sensor as set forth in claim 1, wherein said bladderis formed by a reinforced rubber enveloPe.
 7. A sensor as set forth inclaim 6, wherein said reinforced rubber envelope is defined by a wovenfabric sleeve impregnated with silicone rubber.
 8. A sensor as set forthin claim 6, wherein said envelope has a layer of minute glass ballsbonded to the external surfaces thereof to reduce friction with thesurfaces of the springs engaged thereby.
 9. A sensor as set forth inclaim 8, wherein the surfaces of the springs engaged by the balls arecoated with a high-slippage substance.